This document describes a proposal to conduct a cohort study of 18,000 men, ages 45-64, living in a geographically defined area of metropolitan Shanghai, People's Republic of China. The target population had been previously identified as par of a cohort study of ambient pollution and lung cancer. Over a 21/2 year period, blood nd urine samples and samples and detailed dietary histories will be collected on each subject. Among the major goals of the study are to (1) determine the independent and interactive roles of hepatitis B virus and aflatoxin exposure in the etiology of hepatocellular carcinoma. Evidence of chronic hepatitis B virus infection will be determined by RIA for HBsAg and evidence of aflatoxin exposure will be determined by urine measurements of aflatoxin metabolites and by comparison of individual dietary histories with food surveys of aflatoxin contamination; (2) to determine the independent and interactive roles of intake of salt (as estimated by urinary sodium/creatinine ratios), intake of nitrate and N-nitroso compounds (measured by urinary assays) and vitamin C deficiency (determined by a serum absorbance spectophotometry assay and by the detailed dietary history) in the etiology of stomach cancer; (3) to determine the role of cigarette smoking, alcohol consumption, intake on N-nitroso compounds and beta carotene/vitamin A deficiency (measured by dietary survey and by a high performance liquid chromatography serum assay) n the etiology of esophageal cancer; (4) to determine the role of beta carotene/vitamin A deficiency and any interactive effect with cigarette smoking in the etiology of lung cancer. Follow-up of the cohort will be accomplished through cancer registration by the population-based Shanghai Cancer Registry, routine ascertainment of death certificates, and annual recontact of al cohort members.